CN1191196C - Prepn of sulfur-free low-ash high-purity expanded graphite - Google Patents

Abstract

A kind of preparation method of sulfur-free low ash high-purity expanded graphite is that high-carbon natural flake graphite, nitric acid, acetic anhydride, perchloric acid press high-carbon natural flake graphite: nitric acid: acetic anhydride: perchloric acid=1: 0.5-1.0 : After mixing in a mass ratio of 1-2: 3-7, react at a reaction temperature of 30-50°C for 30-120 minutes to prepare acidified graphite, wash with water, dry, impregnate with a mixed acid of hydrochloric acid and hydrofluoric acid, and remove After acid and drying, expand at 900-1100°C to obtain sulfur-free, low-ash, high-purity expanded graphite. The invention has the advantages of simple preparation method and easy operation, and the prepared high-purity expanded graphite has no sulfur and the ash content is less than 400ppm.

Description

A kind of preparation method of sulfur-free low ash expanded graphite

Technical field:

The invention belongs to a preparation method of expanded graphite, in particular to a preparation method of sulfur-free and low-ash expanded graphite.

Background technique:

Expanded graphite is an intermediate product in the manufacture of flexible graphite. It is a loose and porous worm-like substance obtained from natural flake graphite through oxidation, acidification intercalation, water washing, drying, and high-temperature expansion, also known as graphite worm. Graphite worms can be compressed into flexible graphite without adding any binder, and its strength mainly depends on the mechanical bite force generated by the worm-like expanded graphite after compression. This material not only has the excellent properties of natural graphite itself such as heat resistance, corrosion resistance, electrical conductivity, thermal conductivity, and self-lubrication, but also has properties such as light weight, softness, compressibility, and resilience that natural graphite does not have. Therefore, various strips, plates, and sheets made of expanded graphite have been widely used as various dynamic and static seals in petroleum, chemical, electric power, metallurgy, machinery, aerospace, nuclear industries and other industries. In terms of sealing, it can withstand harsh working conditions. Compared with asbestos and rubber, it has incomparable advantages. It can be called the "King of Sealing" in the contemporary era. ". It is precisely because of this that flexible graphite has attracted the attention of countries all over the world and has developed rapidly.

With the advancement of science and technology and the continuous development of practice, in some high-tech fields, such as aerospace, nuclear power, etc., more and more stringent quality index requirements are put forward for expanded graphite, especially the requirements for sulfur and ash content as low as possible. Due to the current chemical or electrochemical methods used to prepare expanded graphite, sulfuric acid that is easy to intercalate is often used as an intercalation agent, resulting in the sulfur content in expanded graphite often being as high as 3-4%; if sulfuric acid is not used as an intercalation agent, but more Use solid oxidants such as potassium permanganate. These solid oxides are often not easy to clean when washed with water, and consume a lot of water, which pollutes the environment. Part of the solid oxidant that cannot be washed off remains in the graphite worms during high-temperature expansion, thus constituting the secondary ash in the expanded graphite.

Invention content:

The purpose of the present invention is to provide a preparation method of sulfur-free and low-ash expanded graphite.

The purpose of the present invention is achieved in this way, adopting nitric acid-acetic anhydride-perchloric acid-high carbon natural flake graphite system to prepare expanded graphite, in terms of controlling sulfur and ash, one is that the process does not involve sulfur-containing compounds and solid oxides The second is to consider that after the acidified graphite is washed, the mineral matter in the tap water may be brought into this factor. For this reason, the method of soaking the acidified graphite with hydrofluoric acid and hydrochloric acid mixed acid, and then centrifuging out the mixed acid solution is avoided. Therefore, the final prepared expanded graphite does not contain sulfur, while the ash content is lower than 400ppm. The ash content is much lower than the ash content <0.1% specified in the high-purity flexible graphite standard formulated by the United States.

The preparation method of the present invention comprises the steps:

1. After mixing high-carbon natural flake graphite, nitric acid, acetic anhydride, and perchloric acid, react at a reaction temperature of 30-50°C for 30-120 minutes to prepare acidified graphite;

2. The graphite is washed with water, dried, impregnated with a mixed acid of hydrochloric acid and hydrofluoric acid according to the quality of the mixed acid solution is 3-5 times that of natural flake graphite, deacidified, and then dried, and expanded at 900-1100°C to obtain Sulfur-free low-ash high-purity expanded graphite;

Wherein each component mass ratio is:

High-carbon natural flake graphite: nitric acid: acetic anhydride: perchloric acid=1: 0.5-1.0: 1-2: 3-7.

As mentioned above, the mass ratio of hydrochloric acid and hydrofluoric acid in the mixed acid is hydrochloric acid:hydrofluoric acid=1-2:3-4.

As mentioned above, high-carbon natural flake graphite has a carbon content greater than 99.9%.

As mentioned above, the expansion volume of the sulfur-free low-ash high-purity expanded graphite is 200-320ml/g, and the ash content is less than 400ppm.

Compared with the prior art, the present invention has the following advantages:

1. The preparation method is simple and easy to operate.

2. The prepared high-purity expanded graphite is sulfur-free, and the ash content is less than 400ppm.

3. The expansion volume of the prepared high-purity expanded graphite is 200-320ml/g.

Specific implementation:

Example 1

After the carbon content is 99.91% natural flake graphite, nitric acid, acetic anhydride, and perchloric acid are mixed according to high-carbon natural flake graphite: nitric acid: acetic anhydride: perchloric acid = 1: 0.5: 1: 3, at a reaction temperature of 30 ° C , reacted for 30 minutes to prepare acidified graphite; acidified graphite was washed with water, dried, and the mass ratio was hydrochloric acid: hydrofluoric acid=2: 3 mixed acid was immersed in 3 times of natural flake graphite by the quality of mixed acid solution for 10 hours, After deacidification and re-drying, it is expanded at 900°C to obtain sulfur-free, low-ash, high-purity expanded graphite with an expansion volume of 200ml/g and an ash content of 395ppm.

Example 2

After the carbon content is 99.95% natural flake graphite, nitric acid, acetic anhydride and perchloric acid are mixed according to high-carbon natural flake graphite: nitric acid: acetic anhydride: perchloric acid = 1: 0.75: 1.5: 5, at a reaction temperature of 40 ° C , reacted for 60 minutes, and prepared acidified graphite; acidified graphite was washed with water, dried, and the mass ratio was hydrochloric acid: hydrofluoric acid=1: 3 mixed acid was immersed in 4 times of natural flake graphite by the quality of mixed acid solution for 12 hours, After deacidification and re-drying, it is expanded at 1000°C to obtain sulfur-free, low-ash, high-purity expanded graphite with an expansion volume of 260ml/g and an ash content of 350ppm.

Example 3

After the carbon content is 99.96% natural flake graphite, nitric acid, acetic anhydride, and perchloric acid are mixed according to high-carbon natural flake graphite: nitric acid: acetic anhydride: perchloric acid = 1: 1: 2: 7, at a reaction temperature of 50 ° C , reacted for 120 minutes to prepare acidified graphite; acidified graphite was washed with water, dried, and the mass ratio was hydrochloric acid: hydrofluoric acid=1: 3.5 mixed acid was immersed in 5 times of natural flake graphite by the quality of mixed acid solution for 15 hours, After deacidification and re-drying, it is expanded at 1100°C to obtain sulfur-free, low-ash, high-purity expanded graphite with an expansion volume of 320ml/g and an ash content of 315ppm.

Claims (1)

1. a preparation method of sulfur-free low ash expanded graphite, is characterized in that comprising the steps: (1) After mixing natural flake graphite with a carbon content greater than 99.9%, nitric acid, acetic anhydride, and perchloric acid, react at a reaction temperature of 30-50° C. for 30-120 minutes to prepare acidified graphite; (2) The acidified graphite is washed with water, dried, soaked by the mixed acid of hydrochloric acid and hydrofluoric acid according to the quality of the mixed acid solution, which is 3-5 times that of natural flake graphite, deacidified, and then dried at 900-1100 ° C. Obtain expanded graphite with sulfur-free ash content <400ppm; Wherein each component mass ratio is: Natural flake graphite: nitric acid: acetic anhydride: perchloric acid=1: 0.5-1.0: 1-2: 3-7.